// Utility function that allows modes to be combined. The mode given
// as the base argument takes care of most of the normal mode
// functionality, but a second (typically simple) mode is used, which
// can override the style of text. Both modes get to parse all of the
// text, but when both assign a non-null style to a piece of code, the
// overlay wins, unless the combine argument was true, in which case
// the styles are combined.

CodeMirror.overlayParser = function (base, overlay, combine) {
    return {
        startState:function () {
            return {
                base:CodeMirror.startState(base),
                overlay:CodeMirror.startState(overlay),
                basePos:0, baseCur:null,
                overlayPos:0, overlayCur:null
            };
        },
        copyState:function (state) {
            return {
                base:CodeMirror.copyState(base, state.base),
                overlay:CodeMirror.copyState(overlay, state.overlay),
                basePos:state.basePos, baseCur:null,
                overlayPos:state.overlayPos, overlayCur:null
            };
        },

        token:function (stream, state) {
            if (stream.start == state.basePos) {
                state.baseCur = base.token(stream, state.base);
                state.basePos = stream.pos;
            }
            if (stream.start == state.overlayPos) {
                stream.pos = stream.start;
                state.overlayCur = overlay.token(stream, state.overlay);
                state.overlayPos = stream.pos;
            }
            stream.pos = Math.min(state.basePos, state.overlayPos);
            if (stream.eol()) state.basePos = state.overlayPos = 0;

            if (state.overlayCur == null) return state.baseCur;
            if (state.baseCur != null && combine) return state.baseCur + " " + state.overlayCur;
            else return state.overlayCur;
        },

        indent:function (state, textAfter) {
            return base.indent(state.base, textAfter);
        },
        electricChars:base.electricChars
    };
};
